Hence the need for platinum group metals. These could be supplied from terrestrial sources, or from the Moon or asteroids. A large source of these metals would make them more economical for the mass market.
I've done some researching this morning. Ballard, a leading fuel cell manufacturer, says they could mass produce these fuels cells for $73 per kw (2005 prices). Current prices are still quite high, but presumably they are not being mass produced. I am assuming that the prices could be reduced considerably from where they are now.
Update: shortly later: Here's a rich source of links to research the topic.